This invention is related to the automation of direct drive cut-off knives having cut-to-mark control used in producing sheets of corrugated board from a continuous web of such material. A direct drive knife is a cut-off in which the cyclic speeds of the rotary blades are electronically controlled.
More particularly, this invention is related to the control of such knives to effect automatic synchronization of the knife to registration marks on the web following a web splice or order change.
Direct drive cut-to-mark knives are known in the art of producing corrugated sheets from a cntinuous web of paperboard. The knives cut the web in reference to preprinted indicia corresponding to the length of a single sheet. The knives employ an optical sensor to detect registration marks on the web and means to synchronize the knife to cut the web at or in specific relation to the registration marks in order to produce sheets of the proper length. In these prior art direct-drive knives, the desired length of the sheet is entered into the knife's control logic through a keyboard entry. The logic enables the optical sensor for a short time period known in the art as a "window" to scan a narrow portion of the web for the registration mark. The "window" is intended to prevent the optical sensor from producing a spurious cut signal caused by printed material or a blemish on the web which might otherwise be mistakenly identified by the optical sensor as a registration mark.
Heretofore, intervention by an operator has been necessary when the continuous web has been formed of spliced webs, and also when there has been an order change requiring that the knife cut sheets of a different length. This situation is necessitated because the knife will normally not be in synchronization with the registration marks of the spliced web or the new length associated with an order change, resulting in the registration marks not appearing in the knife logic generated "window". Furthermore, the manual adjustment itself results in the temporary cutting of sheets of improper length, resulting in scrap and in some instances in an exceptionally long sheet which may obstruct the sheet-stacking mechanism. A more detailed discussion of the prior art knives, with reference to the drawings to facilitate understanding, follows in the Detailed Description of the Prior Art.
The present invention removes the necessity for an operator-initiated adjustment following a splice or order change. Moreover, the present invention controls the synchronization of the knife with the registration marks of the spliced web or order change in a manner that minimizes scrap and reduces the possibility of an exceptionally long scrap sheet which may obstruct the stacking mechanism.